Michaels was born in Los Angeles, California[2] to JoAnn McKarus[4] and raised in Santa Monica. Michaels has recalled a traumatic childhood that included night terrors, her parents' divorce when she was 12, and suffering verbal abuse by classmates as a 5-foot, 2-inch, 175-pound eighth-grader.[2]

As a personal trainer, Michaels uses a blend of strength training techniques with her clients including kickboxing, yoga, Pilates, plyometrics, and weight training.[5] Since 1993, Jillian has held two personal training certificates from the National Exercise & Sports Trainers Association (NESTA) and The Aerobics and Fitness Association of America (AFAA). In addition, she is Kettlebell Concepts certified. Jillian has also developed a continuing education series for trainers with AFAA and holds a nutrition and wellness consultant certificate with the American Fitness Professionals and Associates (AFPA).[6]

In January 2012, Michaels released a 90-day weight loss program titled "Body Revolution".[7] Michaels' business partner and manager is Giancarlo Chersich. Together, they operate Empowered Media, LLC.[8]

Michaels has released over 15 DVDs since 2005 including Ripped in 30, Extreme Shed and Shred, Killer Buns and Thighs, Kickbox Fastfix (released March 2012), and Killer Abs.

In addition to her DVDs, Michaels has also authored several books on health and wellness topics. Several of these books, including Master Your Metabolism and Unlimited, have made the New York Times Best Seller list.[9][10]

Michaels hosted a Sunday talk radio show on Los Angeles' KFI (640 AM) from 2006 through 2009.[citation needed] Since February 2011, Michaels has hosted a weekly podcast, The Jillian Michaels Show, through iTunes. In December 2011 the show was among the podcasts honored by Apple in its App Store Rewind 2011, winning in the Best New Audio Podcast category.[11]

Michaels was an original trainer on the reality seriesThe Biggest Loser when the show debuted in October 2004. On the show, she assumed the role of Red Team trainer and remained in that capacity for the first two seasons. After her departure in 2006, she was replaced by Kim Lyons.[14] She returned to the show in 2007 as the Black Team trainer competing against Lyons' Red Team and Bob Harper's Blue Team.[15] Along with Harper, Michaels was also a trainer in the Australian version of the show from 2006 to 2008.[16]

On December 7, 2010, Michaels announced via Twitter that the eleventh season of the show would be her last.[17] Michaels made her last appearance on The Biggest Loser in May 2011.

On September 4, 2012, it was announced that Michaels will return to The Biggest Loser in Season 14.[18] Michaels also returned for Season 15, which premiered on October 15, 2013 on NBC.

Michaels announced on June 25, 2014 that she will not be returning for Season 16 which is set to air in the fall of 2014, marking her third departure from the weight loss series.[19]

On May 6, 2011, CBS Television Distribution announced that Michaels had signed a multi-year deal to become a co-host of the panel-discussion show The Doctors, as well as to serve as a special correspondent on the CTD program Dr. Phil. Michaels had been a guest on The Doctors several times previously.[23] On the show, Michaels hosted a recurring segment called Ask Jillian, which dealt primarily with nutrition and diet topics.

Michaels left The Doctors in January 2012 after half a season, because, she claimed, the arrangement "wasn't the fit both the show and I hoped for".[24][25]

Michaels serves as an adviser to the National Day of Dance for Heart Health, an organization that encourages people to exercise.[33] In January 2012, she was a participant in the Clinton Foundation's inaugural "Health Matters: Activating Wellness in Every Generation" conference.[34]

In 2010, Michaels faced four separate lawsuits alleging ingredients in the Jillian Michaels Maximum Strength Calorie Control dietary supplement, the Jillian Michaels Maximum Strength Fat Burner and the Triple Process Total Body Detox and Cleanse, were ineffective or dangerous.[35][36][37] In each instance, Michaels denied the allegations. All four suits were dismissed.[38][39][40]

Michaels was the subject of a critical October 2010 op-ed piece in the Los Angeles Times. The article claimed Michaels "is not actually a real fitness trainer—she's an actress playing the role of fitness trainer on TV and in a line of popular DVDs" and alleged she had let several of her fitness certifications lapse.[41] Michaels responded by threatening legal action for defamation, stating she had been an active physical trainer for 19 years and that none of her certifications have lapsed.[42] The newspaper published a correction citing her up-to-date certifications shortly thereafter and no legal action was taken.[43]

Michaels has two children with her partner Heidi Rhoades.[44] Michaels adopted their then-two-year-old daughter from Haiti in May 2012, and Rhoades gave birth to a son that same month.[45] On her sexuality, Michaels has stated, "Let's just say I believe in healthy love. If I fall in love with a woman, that's awesome. If I fall in love with a man, that's awesome. As long as you fall in love…it's like organic food. I only eat healthy food, and I only want healthy love!"[44]